1. Field of the Invention
The present invention relates generally to a transducer system for the measurement of blood pressure or other fluid pressure. In particular, the present invention relates to a fluid pressure transducer apparatus that incorporates reusable sensor components with disposable fluid path components, and which is easily calibrated for accurate fluid pressure monitoring.
2. Background Technology
For many medical applications, it is important to monitor bodily fluid pressures such as blood pressure. There are generally two types of methods used for measuring and/or monitoring blood pressure, namely indirect and direct methods. Indirect measurements are based on non-invasive procedures such as using a pressure cuff and a stethoscope. Direct pressure measurements are, in contrast, made by using invasive techniques that have the advantages of providing more accurate, more continuous, and if desired, more localized pressure monitoring.
For direct blood pressure measurement and monitoring, typically a catheter is inserted into a blood vessel and is connected to tubing that in turn is connected to a pressure transducer. The transducer includes a sensor that senses the pressure of the fluid path and converts the pressure therein to electrical signals which correspond to the quantity of pressure. The electrical signals are transmitted to a monitor and/or other output devices that display the patient""s blood pressure.
With rising health care costs there has been a drive towards developing more cost-effective devices for measuring blood pressure. This has led to the development of disposable blood pressure transducers. Disposable systems typically include a pressure sensor, cable, plastic housing, stopcock, flush device, and associated tubing which are assembled together and provided to the hospital or medical care provider in a sterile package. Such a system is intended for a single patient use, following which the entire assembly is disposed of. The average manufacturing cost of this type of system is fairly high, with the pressure sensor and cable representing the two most costly components. Therefore, any improvements in this type of system with the aim of reduced costs will tend to focus on these two components, specifically evaluating the necessity of disposing this portion of the system following each use.
Reusable transducer systems have been developed that comprise a two-component system in which the relatively expensive sensor on a faceplate is reusable, while the other component with the patient-contacting fluid path is disposable. In these types of systems, each component is provided with a diaphragm that closes off access to the fluid path and the sensor, respectively. In order to measure pressure in the fluid path, the disposable component is attached to the reusable faceplate component with the diaphragms in a confronting and pressure communicating relationship to thereby communicate pressure from the fluid path to the sensor. These two-component transducer systems typically have the disposable fluid path component, usually referred to as the fluid dome, rotatably coupled to the reusable sensor portion. The components are typically secured together by threaded interaction to bring the diaphragms into confronting and pressure communicating relationship by relative rotation between the dome and the reusable component and their respective diaphragms. After use, the disposable unit is removed from the reusable part and discarded, and may be replaced with a new and sterile unit.
Examples of blood pressure measuring devices that are reusable are described in U.S. Pat. Nos. 5,752,918; 5,868,678; 4,920,972; 5,993,395; and 6,117,086. There are also commercially available reusable blood pressure measuring devices such as the LogiCal(trademark) transducer system manufactured by Medex, and the BioTrans(trademark) transducer system manufactured by Biosensors International. These systems have addressed the problems of cost containment through reuse of the sensor and cable; however, all of these systems generally exhibit the following problems: (1) unpredictable failure time due to an unspecified life cycle of the reusable faceplate; (2) inventory level management problems as a result of the unspecified reusable life cycle; (3) sensor inaccuracy and calibration costs; (4) lack of a convenient calibration method for the end user; and (5) obstructed fluid path visibility in the region of the disposable/reusable diaphragm interface.
More specifically, regarding the first problem described above, there are limitations to the expected lifetime of the reusable faceplate component which are caused by wear associated with multiple disposable dome attachments to the reusable faceplate, particularly in the location of the disposable dome interface with the reusable sensor. The lifetime of the device is also limited by the effects of material degradation from alcohol or detergent cleansing of the reusable faceplate and sensor diaphragm surface following each use. Unpredictable failure of the reusable component is a serious problem in medical applications where a patients"" lives are frequently in jeopardy.
The second problem described above concerns the inventory management problems that can arise from a blood transducer device having an unknown reusable component lifetime. A hospital or medical care provider may overstock the replacement faceplates to ensure the availability of these components. This approach, however, counteracts the cost advantages of using a reusable system due to the need to carry excessive inventory. Alternatively, the possibility of not carrying sufficient inventory may result in the loss of a critical device in an emergency situation.
The third problem described above is associated with sensor accuracy and calibration costs. Current iterations of the two component reusable systems use a sensor module identical to those used in traditional disposable systems, which have been pre-calibrated to meet the performance specifications of the disposable systems. A shift in sensor performance is typically observed following assembly of the sensor into the reusable package. The reusable system manufacturer is able to correct for some of the performance shifts that occur following packaging, but usually does not have the expertise required to adjust all of the affected parameters. As a result, these manufacturers are frequently confronted with yield losses associated with out of specification performance and/or non-optimized performance. Furthermore, each sensor must be re-calibrated on an individual basis after packaging into the device housing, which greatly increases costs and time required for individual testing of each assembled device.
The fourth problem with prior systems concerns the difficulties in calibration or functionality tests for an end user. The traditional calibration methods have usually been either (1) front side pressure application; (2) back side pressure application; or (3) electronic calibration. Front side calibration typically consists of attaching a pressure generating device such as a syringe to the fluid filled side of the transducer and monitoring the transducer output for proper response. The disadvantages of front side calibration are that the system must be primed with fluid prior to the test, and that the pressure mechanism must interact with the sterile fluid pathway, which requires significant effort to ensure that the fluid pathway is not contaminated. Back side calibration differs from front side calibration by applying pressure to the non-sterile side of the transducer, which avoids the problems of sterility violation and is the method currently utilized by several manufacturers.
Electronic calibration and functionality testing are performed without the use of a pressure source. A resistive network is interconnected with the electronic circuitry of the sensor and/or cable via a user operated switch which creates a predictable change in the sensor""s output. This method has the advantage of eliminating any need for a pressure generating device, but only tests the electrical connectivity of the system, as opposed to the front and back side testing which include a mechanical exercising of the diaphragm, thereby providing a more thorough testing of functionality. One of the current devices on the market, the Medex LogiCal(trademark) system, can be tested through front side calibration and also incorporates an electronic calibration test switch with the reusable portion of the device. This approach has the disadvantage of incurring additional costs in the reusable component through the inclusion of a user activated switch and an additional resistor, plus the associated wiring.
The fifth problem associated with prior two-component reusable fluid pressure monitoring systems arises from the inability to view the fluid path in the area directly above the interface of the reusable sensor and the disposable dome. Initially, the system needs to be filled with saline solution and air bubbles must be eliminated prior to patient use. Air bubbles in the system not only degrade the accuracy of the device as a result of unwanted signal dampening, but also present a significant safety problem for the patient. For example, the introduction of air into the cardiovascular system may result in possible embolism. An area of particular concern is the area surrounding the disposable dome and reusable sensor interface. This area tends to contain an uneven surface between the diaphragms that promotes the formation of bubbles and also inhibits the flushing out of these bubbles during the saline solution fill operation. The reusable sensor diaphragms in the LogiCal(trademark) transducer system and the BioTrans(trademark) transducer system are circular, with input and output ports positioned in the area of the reusable to disposable dome interface, thus obstructing visibility in the most critical areas of air bubble formation.
Therefore, there is a need for a reusable blood pressure transducer system that overcomes the above problems and disadvantages.
It is a primary object of the invention to provide a system for the direct measurement of fluid pressure that includes a disposable dome component and a reusable base component.
Another object of the invention is to provide a blood pressure monitoring apparatus having a usage indicator which is advanced with each disposable dome attachment and intended to provide a visual indication of reusable base usage within a qualified number of uses, thereby avoiding the problem of unpredictable failure due to an unspecified lifetime for a reusable component.
A further object of the invention is to provide a reusable pressure transducer that is accurate, and inexpensive to manufacture and calibrate.
It is yet another object of the invention to provide a reusable blood pressure monitoring apparatus that enhances fluid flow visibility in the region of the disposable dome to reusable sensor interface to aid the user in assuring air bubble elimination during the system saline fill process.
It is a further object of the invention to provide a reusable blood pressure monitoring apparatus having a self-registering hinge and latch interface between the disposable and reusable components which is ergonomically beneficial to the user.
Another object of the invention is to provide a reusable blood pressure monitoring apparatus having a calibration port through which pressure may be applied to the sensing element for calibration/functionality testing without contacting the sterile disposable component of the apparatus.
To achieve the forgoing objects, and in accordance with the invention as embodied and described herein, an apparatus is provided for fluid pressure monitoring in medical applications such as monitoring of blood pressure. The apparatus includes a reusable base section, and a disposable dome section detachably connected to the base section and adapted to be coupled to a patient. The disposable dome section defines a fluid pathway and includes a dome viewing segment in fluid communication with a flush segment and a stopcock segment. The disposable dome and associated diaphragm have a geometry such that the input and output ports are sufficiently far from the critical viewing area to greatly enhance the fluid flow visibility in the fluid pathway, thereby reducing the risk of introducing harmful air bubbles into a patient""s bloodstream.
A pressure transducer sensor is disposed in the reusable base section and is adapted to produce electrical signals proportional to fluid pressures sensed in the fluid pathway. The design of the pressure sensor ensures accuracy and minimal calibration of the device. A usage indicator is disposed in the base section to provide a visual indication of usage of the apparatus within a predetermined number of uses. This allows the operator to determine whether or not the number of uses of the apparatus is within the specified recommended limit. A calibration port can be provided in the base section to allow for simple calibration by the user without violating the sterility of the apparatus. The ability to reuse the base section with the sensor component reduces the cost of the apparatus, while the disposability of the dome section with the fluid pathway ensures sterility for each patient use.
These and other objects and features of the present invention will become more fully apparent from the following description, or may be learned by the practice of the invention as set forth hereinafter.